The proposed work deals with developing and calibrating procedures for using electron microscope autoradiography quantitatively at the highest possible resolution. This involves determining the parameters that affect resolution for isotopes differing in energy, such as 125I, 14C, 3H and 32P. For the latter isotope we will attempt to develop a track autoradiographic procedure to optimize the use of very high energy. Procedures for soluble compound autoradiography are also being investigated.